The present invention relates to a process for the fractional crystallization of lipids from solvent. Most often the lipid is separated into fractions according to the degree of saturation or acylation of the fractions. In general such fractional crystallization is carried out by dissolving the lipid in a solvent, cooling the resulting solution until a crystalline fraction is formed, and separating the resulting crystalline fraction from remaining liquor. Often the liquor is subjected to a repeat of this process at a lower temperature to obtain one or more additional lipid fractions. Conventionally a lipid crystal crop is separated from its liquor by filtration, most generally using large rotary vacuum filters. These filters constitute a very large investment item in a commercial production plant.
The present invention provides a process for recovering the crystalline fraction from the lipid/solvent solution in relatively simple and efficient fashion. It is based in part on the discovery that a heap of crystals or melt thereof can be accumulated from and in the presence of cold solvent without the crystals tending to redissolve in the solvent, provided that the solvent has been substantially depleted of dissolved lipid. Accordingly, the present invention provides for crystallization of lipid fed to the process concurrently with washing of the previously like-formed lipid crystals in especially efficient fashion which advantageously is done by establishing a countercurrent flow relationship between fresh solvent and the lipid crystals to be recovered, i.e., so the crystals being recovered are contacted with the solvent leanest in dissolved lipid.